The invention herein relates to friction materials. More particularly, it relates to friction materials having low abrasion which are useful as brake shoes for railroad rolling stock with relatively soft steel wheels.
Brake shoes for railroad brakes have been made of two types of materials. Older American and European railroad cars, and some modern European railroad cars, have brake shoes made of cast iron. Most American rolling stock of recent vintage, however, has composition brake shoes made of highly leaded materials such as those described in U.S. Pat. Nos. 2,686,140; 2,861,964; 3,152,099 and 3,390,113. As noted in these patents, the composition brake shoes offer a number of advantages over the older cast iron shoes.
With softer steel railroad car wheels, however, the composition material brake shoes of the prior art have often proved unsatisfactory, because they are usually quite abrasive. This is particularly true in European countries, where it has been customary to manufacture wheels from softer grades of steel and to forego the heat treating and hardening steps used in the manufacture of most American wheels. Only a few specific formulations have been found to have sufficiently low abrasion for use with the softer steel wheels.
It is therefore an object of this invention to provide a composition material having consistently low abrasive characteristics and suitable for use as brake shoes for railroad cars with relatively soft steel wheels.